Gear and Rolling Dies for Forming Gear

ABSTRACT

A gear including a gear shaft, and a gear wheel made of a resin material, the gear wheel being fixed to the gear shaft by molding. The gear having a plurality of concave portions and convex portions that repeat in a circumferential direction. The plurality of concave and convex portions are arranged such that they extend in the axial direction of the gear shaft, and arranged such that the convex portions of one concave and convex group are adjacent to the concave portions of the other concave and convex group. Due to the relative displacement of the concave portions and the convex portions, stepped portions are formed at a boundary between the concave and convex groups in the circumferential direction of the gear shaft.

TECHNICAL FIELD

The present invention relates to the technical fields of a gear obtained by molding a gearwheel such as a worm gear on a rotation shaft including a drive shaft of a wiper motor provided in a vehicle, and rolling dies for forming a gear.

BACKGROUND ART

A drive shaft to be provided in a wiper motor will be described herein as an example of a gear shaft. In a metal-made drive shaft, a resin-made worm gear (corresponding to a gearwheel) is insert-molded. The worm gear (or gearwheel) needs to be fixed to the drive shaft so as not to come off and not to rotate with respect to the drive shaft. Therefore, conventionally, on an outer peripheral surface onto which the boss of the worm gear of the drive shaft is fitted, a serration groove engraved so as to have repeated concavities and convexities circumferentially and a concave groove-like slit in a ring shape in the circumferential direction engraved at an intermediate portion in the axial direction of the serration groove are provided, and the worm gear is prevented from rotating circumferentially by the serration groove, and prevented from coming off by restricting the coming off (slipping) thereof in the axial direction by the slit (for example, Patent Document 1).

Patent Document 1: Japanese Published Examined Patent Application No. S63-53406

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, in the conventional technique, the width of the slit is narrow (because the length in the axial direction is short), so that a retaining strength sufficient to prevent the coming off cannot be secured. Therefore, it has been suggested that the width of the slit is widened or a plurality of slits are provided in the axial direction to increase the retaining strength, however, in this case, the groove length in the axial direction of the serration groove becomes short and the strength for preventing rotation lowers. Therefore, it is suggested that the gear is made thick and the axial lengths of the slit and the serration groove are secured so as to correspond to the necessary strength or the outer diameter of the serration is made larger than the shaft, however, in this case, the entirety becomes large in size or the shaft outer shape machining becomes complicated. These are the problems that the present invention intends to solve.

Means for Solving the Problem

In view of the above-described circumstances, the present invention was made to solve the problem, and according to a first aspect of the invention, a gear comprising a gear shaft and a gear wheel made of a resin material, the gear wheel fixed to the gear shaft by molding, wherein a plurality of concave and convex groups having concave portions and convex portions repeatedly in the circumferential direction are formed in the axial direction on the outer peripheral surface of the gear shaft at a portion to which the gear wheel is fixed, adjacent concave and convex groups are disposed so as to arrange convex portions of one concave and convex group adjacent to concave portions of the other concave and convex group, and stepped portions are formed at the boundary between the concave and convex groups.

According to a second aspect of the invention, in the first aspect, the concave and convex groups are serration grooves having concave portions and convex portions repeated at the same pitches, and adjacent serration grooves are provided so as to make their phases different from each other.

According to a third aspect of the invention, in the first aspect, the adjacent concave and convex groups are serration grooves having concave portions and convex portions repeated at pitches different from each other.

According to a fourth aspect of the invention, in any one of the first through third aspects, the adjacent concave and convex groups are simultaneously formed by form rolling.

According to a fifth aspect of the invention, in any one of the first through third aspects, one of the adjacent concave and convex groups is formed by first form rolling, and the other is formed by second form rolling after forming the one concave and convex group.

According to a sixth aspect of the invention, in any one of the first through fifth aspects, inclined end faces reaching the concave portions are formed on the stepped portions.

According to a seventh aspect of the invention, when forming concave and convex groups having concave portions and convex portions repeated circumferentially on the outer peripheral surface of a gear shaft on a portion to which a gearwheel of a gear is fixed by molding by using a plurality of rolling dies having convex portions and concave portions, said convex portions facing the concave portion of the concave and convex groups and said concave portions facing the convex portions thereof, adjacent rolling dies roll on the outer periphery of the gear shaft in a state that the concave portions and convex portions are adjacent to each other in the axial direction.

According to an eighth aspect of the invention, in the seventh aspect, on the ends at which the rolling dies are adjacent to each other, notched surfaces are formed by slantingly notching the tip ends of the convex portions.

According to a ninth aspect of the invention, in either the seventh or eighth aspect, the notched surfaces are formed by notching portions from the tip ends of the convex portions to intermediate portions between the convex portions and the concave portions.

According to a tenth aspect of the invention, in any one of the seventh through ninth aspects, the plurality of rolling dies are integrated together so that a plurality of concave and convex groups on the outer periphery of a gear shaft are formed by one form rolling process.

EFFECT OF THE INVENTION

According to the first aspect of the invention, at the boundary between the adjacent concave and convex groups of the gear shaft, stepped portions are formed due to relative displacement of the concave portions and the convex portions, and this functions to prevent coming-off of the gearwheel, and even if a slit is not formed in the gear shaft, reliable and firm prevention of rotation and prevention of coming-off are realized.

According to the second or third aspect of the invention, the reliable and firm prevention of rotation and prevention of coming-off are easily realized by forming the serration groove.

According to the fourth aspect of the invention, concave and convex groups with pitches different from each other in the circumferential direction can be easily formed by one form rolling process.

According to the fifth aspect of the invention, the shape of the stepped portion at the boundary of the concave and convex groups becomes complicated, so that the coming-off preventive effect can be increased.

According to the sixth aspect of the invention, filling of a resin material is reliably performed, and the gearwheel can be more reliably and firmly integrated with the gear shaft.

According to the seventh aspect of the invention, formation of a slit becomes unnecessary, and the machining efficiency of the gear shaft can be increased.

According to the eighth aspect of the invention, filling of a resin material when molding a gearwheel in a gear shaft can be effectively performed and the gearwheel can be more reliably and firmly integrated.

According to the ninth aspect of the invention, the coming-off preventive effect for the gearwheel is not lost, and filling of the resin material when molding the gearwheel in the gear shaft can be effectively performed.

According to the tenth aspect of the invention, a plurality of concave and convex groups can be formed by one form rolling process, and the machining efficiency can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional front view of a drive shaft;

FIG. 2 shows the drive shaft alone, wherein FIG. 2(A) is an enlarged side view of a main portion, FIG. 2(B) is a developed front view of the main portion, and FIG. 2(C) is a front view describing a form rolling process by using rolling dies;

FIG. 3 is a main portion perspective view of the drive shaft;

FIG. 4 is an enlarged side view of a main portion of a drive shaft alone according to a second embodiment; and

FIG. 5 is a main portion enlarged front view describing a form rolling process of a drive shaft alone according to a third embodiment by using rolling dies.

DESCRIPTION OF THE SYMBOLS

-   1 drive shaft -   2 worm gear -   3 first serration groove -   3 a convex portion -   3 b concave portion -   4 second serration groove -   4 a convex portion -   4 b concave portion -   5 first rolling die

Best Mode for Carrying Out the Invention

Next, embodiments of the present invention will be described with reference to the accompanying drawings.

In the drawings, the reference numeral 1 denotes a drive shaft (corresponding to the gear shaft of the present invention) of a wiper motor, and onto one end of the drive shaft 1, a boss 2 b of a worm gear 2 (corresponding to the gearwheel of the present invention) including gear teeth 2 a engraved on its outer periphery is integrally fitted and supported to form the gear of the present invention. The worm gear 2 corresponding to the gear teeth of the gear is formed in a state integrated with the drive shaft 1 by means of molding by filling a resin material into a space of a mold by a method such as injection molding on one end of the drive shaft 1. As conventionally, the worm gear 2 is formed so that the gear teeth 2 a engage with a worm engraved on a motor output shaft that is not shown, and the worm gear rotates in an interlocked manner with the motor driving.

The drive shaft 1 is structured as follows in a first embodiment. That is, on one end of the drive shaft 1 onto which the worm gear boss 2 b is fitted, first and second serration grooves (corresponding to concave and convex groups of the present invention) 3, 4 in parallel in the axial direction are engraved. These first and second serration grooves 3, 4 are formed so as to have the same diameter. The first serration groove 3 is formed on a half of one end in the axial direction of the boss 2 b fitting portion, and has a length half the fitting length in the axial direction of the boss 2 b, and have triangular (other irregular shapes such as quadrilateral shapes are possible, of course) convex portions (mountain portions) 3 a and concave portions (valley portions) 3 b repeated at predetermined pitches in the circumferential direction on the outer peripheral surface of the drive shaft 1.

On the other hand, the second serration groove 4 is formed on the other half in the axial direction of the portion on which the boss 2 b of the drive shaft 1 is fitted, and has a length half the fitting length of the boss 2 b in the axial direction, and is engraved so that convex portions 4 a and concave portions 4 b similar to those of the first serration groove 3 are repeated circumferentially at the same pitches as in the first serration groove 3. The second serration groove 4 is engraved so as to shift (displace) its phase circumferentially by a ½ pitch from the first serration groove 3. Namely, the first and second serration grooves 3, 4 are arranged in a state that second serration groove concave portions 4 b are adjacent to the first serration groove convex portions 3 a in the axial direction and the second serration groove convex portions 4 a are adjacent to the first serration groove concave portions 3 b in the axial direction. Thereby, at the boundary between the first and second serration grooves 3, 4 (end faces orthogonal to the axial direction), stepped portions S based on the difference between the inner diameters of the convex portions 3 a, 4 a and the concave portions 3 b, 4 b are integrally formed in the circumferential direction of the drive shaft 1, the stepped portions S function similarly to the slit and prevents the worm gear 2 formed by molding from coming off the drive shaft 1.

Next, a method for forming the serration grooves 3, 4 on the drive shaft 1 will be described. In this embodiment, the first and second serration grooves 3, 4 are simultaneously formed by one form rolling.

That is, the first and second serration grooves 3, 4 are formed by form rolling by using cylindrical first and second rolling dies 5, 6 having grooves formed on the outer peripheral surfaces, corresponding to the serration grooves 3, 4, and on the outer peripheries of the first and second rolling dies 5, 6, similar to the forming pitches of the convex portions 3 a, 4 a and the concave portions 3 b, 4 b of the first and second serration grooves 3, 4, concave portions 5 a, 6 a and convex portions 5 b, 6 b facing said convex and concave portions of the serration grooves are formed to be long in the axial direction. Furthermore, on both sides in the axial direction of the convex portions 5 b, 6 b, there are notches slantingly from the tip ends of the convex portions 5 b, 6 b to the sections between the convex portions 5 b, 6 b and the concave portions 5 a, 6 a, that is, to the intermediate portions reaching the concave portions 5 b, 6 b, whereby inclined notched surfaces 5 c, 6 c are formed on the sides of the convex portions 5 b, 6 b and orthogonal surfaces 5 d, 6 d orthogonal to the axial direction of the rolling dies 5, 6 are formed on the sides of the concave portions 5 a, 6 a. In this embodiment, the first and second rolling dies 5 and 6 are integrated so that the first rolling die convex portions 5 a and the second rolling die concave portions 6 b are arranged in a line in the axial direction, and by performing form rolling by pressing these dies against the drive shaft 1, the first and second serration grooves 3, 4 are formed on the drive shaft 1 by one form rolling. Thereby, on the drive shaft 1, as described above, concave portions 3 b of the first serration groove 3 and the convex portions 4 a of the second serration groove 4 are formed so as to be arranged in a line in the axial direction, and at the boundary between the first and second serration grooves 3, 4, stepped portions S are formed.

Thus, when the drive shaft 1 is form-rolled by using the first and second rolling dies 5, 6, the groove depths of the first and second serration grooves 3, 4 are formed so as to correspond to the groove depths from the convex portions 5 b, 6 b of the first and second rolling dies 5, 6 to the concave portions 5 a, 6 a. On the adjacent ends of the first and second rolling dies 5, 6, inclined notched surfaces 5 c, 6 c are formed on the convex portion side from the convex portions 5 b, 6 b to the concave portions 5 a, 6 a, and on the sides of the concave portions 5 a, 6 a, orthogonal surfaces 5 d, 6 d are formed. Therefore, at the boundary at which the first and second serration grooves 3, 4 are adjacent to each other, as shown in FIG. 2(B), on the ends of the tip end sides (outer diameter sides) of the serration groove convex portions 3 a, 4 a, orthogonal end faces 3 c, 4 c orthogonal to the axial direction of the drive shaft 1 are formed based on the die orthogonal surfaces 5 d, 6 d, and on the sides of the serration groove concave portions 3 b, 4 b on the inner diameter sides, inclined end faces 3 d, 4 d are formed so as to be continued to adjacent convex portions 4 a, 3 a based on the first and second rolling die notched surfaces 5 c, 6 c.

Thereby, when a worm gear 2 is formed by molding on one end of the drive shaft 1, because the resin material is guided so as to flow into the concave portions 3 b, 4 b through the inclined end faces 3 d, 4 d, the integration between the resin material and the drive shaft 1 becomes reliable and the integration in the circumferential direction becomes firm, and in addition, the worm gear 2 is reliably prevented from coming off in the axial direction by the orthogonal end faces 3 c, 4 c.

In the developed view of one end of the drive shaft 1 of FIG. 2(B), the mountain folds as the peaks of the convex portions 3 a, 4 a are shown by solid lines, and valley folds as bottoms of the valleys of the concave portions 3 b, 4 b are shown by dotted lines.

In the first embodiment constructed as described above, the worm gear 2 is reliably prevented by the first and second serration grooves 3, 4 from rotating, and at the boundary between the groves 3, 4, the convex portions 3 a, 4 a are positioned between the concave portions 4 b, 3 b of the other groove, and the end faces thereof are exposed in a staggered manner on both sides to form steps when they are viewed in the axial direction. Then, the staggered exposed end faces (steps) function to prevent the worm gear 2 from coming off, and as a result, even without engraving the conventional slit, the worm gear 2 can be prevented from coming off the drive shaft 1 by a high strength. Then, according to needlessness of formation of the slit, the length of the drive shaft 1 can be shortened, and this can contribute to compact construction.

In addition, in this construction, by form rolling in a state that the first and second rolling dies 5, 6 are phase-shifted, phase-shifted serration grooves 3, 4 can be easily formed, and it becomes unnecessary to engrave the concave groove-like slit, so that the machining efficiency is improved.

Furthermore, in this construction, because notched surfaces 5 c, 6 c and orthogonal surfaces are formed on the rolling dies, orthogonal end faces 3 c, 4 c on the sides of the convex portions 3 a, 4 a are formed at the boundary between the first and second serration grooves 3, 4, and inclined end faces 3 c, 4 c are formed on the sides of the concave portions 3 b, 4 b, and when the worm gear 2 is formed by molding, the resin material is filled so as to be guided to the sides of the concave portions 4 b, 3 b by the inclined end faces 3 d, 4 d, so that the worm gear 2 is reliably and firmly integrated. On the sides of the convex portions 3 a, 4 a, because orthogonal end faces 3 c, 4 c are formed, the worm gear 2 is reliably prevented from coming off the drive shaft 1, and therefore, an excellent gear can be provided.

In this construction, by form rolling by integrating the first and second rolling dies 5 and 6, the first and second serration grooves 3, 4 can be formed by one form rolling, and the machining efficiency can be further improved.

The present invention is not limited to the above-described embodiment, and as in the case of the second embodiment shown in FIG. 4, when the first and second convex and concave groups (serration grooves) 7, 8 are formed on the drive shaft, even if the circumferential pitches of the convex portions 7 a, 8 a and the concave portions 7 b, 8 b are made different from each other, by making the convex portions and concave portions 7 a, 8 b, and 8 a, 7 b adjacent to each other in the axial direction, stepped portions can be formed in the circumferential direction.

Furthermore, the third embodiment shown in FIG. 5 is also possible. In this embodiment, the first concave and convex group 9 to be formed on the drive shaft 1 is formed by form rolling by using the first rolling die 10, and thereafter, the second concave and convex group 11 is formed by form rolling by using the second rolling die 12 so as to shift the phase by ½ at the same pitches. In this case, on the first and second rolling dies 10, 12, as in the case of the first embodiment, inclined notched surfaces 10 a, 12 a are formed. In this construction, the notched surfaces 10 a, 12 a are entirely inclined surfaces from the convex portions 10 b, 12 b to the concave portions 10 c, 12 c. Thereby, as shown in FIG. 5, at the boundary between the first and second convex portions 9 a, 11 a, inclined portions 9 c, 11 c are formed to reach the concave portions 11 b, 9 b. In this case, by form rolling by setting the first die 10 for forming the first concave and convex group 9 and the second die 12 for forming the second concave and convex group 11 in a positional relationship in which they overlap at the boundary, steps due to the shifting in the axial direction can be formed at the boundary, and in this case, the integrating strength in the rotation stopping direction can be further increased.

The number of concave and convex groups to be arranged in the axial direction are not necessarily two, and may be set to 3 or more if necessary, and as the number increases, the number of boundaries increases and the higher coming-off preventive function is obtained. Furthermore, the plurality of concave and convex groups may be formed while being made different in length in the axial direction.

INDUSTRIAL APPLICABILITY

A gear and rolling dies for forming the gear of the invention are useful for a drive shaft of a wiper motor to be provided in a vehicle, and in particular, effective in the case where high strength is necessary to prevent the worm gear from coming off and rotating. 

1. A gear comprising a gear shaft; and a gear wheel made of a resin material, the gear wheel being fixed to the gear shaft by molding, wherein: a plurality of concave and convex groups, having concave portions and convex portions that repeat in a circumferential direction are formed in an axial direction on peripheral surface of the gear shaft at a portion to which the gear wheel is fixed, adjacent concave and convex groups are disposed so as to arrange convex portions of one concave and convex group adjacent to concave portions of the other concave and convex group, and stepped portions are formed at a boundary between the concave and convex groups.
 2. The gear according to claim 1, wherein the concave and convex groups are serration grooves that have the concave portions and the convex portions repeated at a same pitch and adjacent serration grooves are provided such that phases of the adjacent serration grooves are different from each other.
 3. The gear according to claim 1, wherein the adjacent concave and convex groups are serration grooves that have the concave portions and the convex portions repeated at different pitches.
 4. The gear according to claim 1, wherein the adjacent concave and convex groups are simultaneously formed by form rolling.
 5. The gear according to claim 1, wherein the one concave and convex group of the adjacent concave and convex groups is formed by first form rolling, and the other concave and convex group is formed by second form rolling after forming the one concave and convex group.
 6. The gear according to claim 1, wherein inclined end faces reaching the concave portions are formed on the stepped portions.
 7. Rolling dies for forming gear that includes a plurality of concave and convex groups having concave portions and convex portions repeated circumferentially on an outer peripheral surface of a gear shaft on a portion to which a wheel of a gear is fixed by molding, the rolling dies comprising: adjacent rolling dies that are formed in an axial direction, wherein: a first rolling die of the adjacent rolling dies having convex portions and concave portions, a second rolling die of the adjacent rolling dies having convex and concave portions, the first rolling die and the second rolling die are positioned such that the convex portions of the first rolling die are arranged adjacent to the concave portions of the second rolling die.
 8. The rolling dies for forming the gear according to claim 7, wherein notched surfaces are formed on ends of the first rolling die and the second rolling die by slantingly notching tip ends of the convex portions.
 9. The rolling dies for forming the gear according to claim 7 wherein notched surfaces are formed by notching portions from tip ends of the convex portions to intermediate portions between the convex portions and the concave portions.
 10. The rolling dies for forming the gear according to claim 7, wherein the plurality of rolling dies are integrated together, and the plurality of concave and convex groups on the outer a peripheral surface of the gear shaft are formed by a form rolling process.
 11. The rolling dies for forming the gear according to claim 7, wherein orthogonal surfaces, which are orthogonal to the axial direction of the first rolling die and the second rolling die, are formed on sides of the concave portions of the first rolling die and the second rolling die.
 12. The rolling dies for forming the gear according to claim 7, wherein the plurality of rolling dies are separate from each other, and one of the plurality of concave and convex groups on the outer peripheral surface of the gear shaft is formed by a first form rolling process, and the other of the plurality of concave and convex groups is formed by a second form rolling process that is preformed subsequent to the first form rolling process.
 13. The gear according to claim 1, wherein the convex portions include orthogonal end faces that are formed on an end at which the boundary between the adjacent concave and convex groups is formed.
 14. The gear according to claim 1, wherein the concave portions include inclined end faces that are formed on sides of the concave portions and are continuous with adjacent convex portions.
 15. The gear according to claim 1, wherein the adjacent concave and convex groups are offset by a half pitch.
 16. A gear comprising: a gear shaft; and a gear wheel made of a resin material, the gear wheel being fixed to the gear shaft by molding, wherein the gear shaft includes: a first serration groove having convex and concave portions; and a second serration groove having convex and concave portions with the second serration groove being offset from the first serration groove in an axial direction, wherein the convex and concave portions of the first and second serration grooves are repeated at a same pitch in a circumferential direction on an outer peripheral surface of the gear shaft, wherein stepped portions are formed at a boundary between the first serration groove and the second serration groove in the circumferential direction of the gear shaft.
 17. The gear according to claim 16, wherein a phase of the second serration groove is shifted by a half pitch from the first serration groove.
 18. The gear according to claim 16, wherein the first serration groove and the second serration groove are arranged so that the concave portions of the second serration groove are adjacent to the convex portions of the first serration groove.
 19. The gear according to claim 16, wherein the convex portions include orthogonal end faces that are formed at the boundary.
 20. The gear according to claim 16, wherein the concave portions include inclined end faces that are formed on sides of the concave portions and are continuous with adjacent convex portions. 